Recently, a reproducing velocity converting technique for a sound signal has been put to practical use. In the technique, the sound signal is converted into a digital signal and the digital signal is recorded in recording media. The digital signal is then converted and output without changing an interval of the sound signal. A speech velocity converting system such as a TDHS (time domain harmonic scaling) system and a PICOLA (pointer interval control overlap and add) system is often used so as to achieve the technique.
The reproducing velocity converting apparatus which embodies the conventional speech velocity converting system will be described below with reference to the accompanying drawings.
FIG. 13 is a block diagram showing a construction of the conventional reproducing velocity converting apparatus.
As shown in FIG. 13, an input sound signal 1a is first transmitted from a sound signal storage memory 1 to a speech velocity converter 4. Next, a speech velocity converted sound signal 1e is calculated in the speech velocity converter 4. The speech velocity converted sound signal 1e is recorded in an output sound signal storage memory 6. The above processing is performed so as to obtain the velocity converted sound signal.
A speech velocity conversion in the above conventional reproducing velocity converting apparatus is accomplished by windowing a sound in accordance with pitch information as to the sound signal and by overlapping adjacent two data, each having a pitch period. An unvoiced sound part of the sound signal is performed in the same way as a voiced sound part. By the way, the sound signal is characterized by that the voiced sound part has a relatively steady waveform at the pitch period but the unvoiced sound part has the non-steady waveform. Thus, since the voiced sound part has the relatively steady waveform, the original waveform is difficult to deform even if the conventional speech velocity converting system is used. Disadvantageously, since the unvoiced sound part does not have the steady waveform, the original waveform is deformed after the speech velocity conversion.